Peltier control circuit and a peltier device structure

ABSTRACT

A Peltier control circuit detects a temperature of a device combined with a Peltier device and controls a current flowing through the Peltier device so as to keep the temperature of the device at a predetermined value. The circuit has a temperature sensing section for detecting the temperature of a device, a comparing section for comparing a temperature detection value with a predetermined temperature reference value, a limiting section for providing a comparison output with the limitation of a current flowing through the Peltier device and providing the limitation with a predetermined temperature characteristics, and a driving section for providing the Peltier device with an input or output driving current in accordance with the comparison output via the limiting section.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Peltier device and a control circuitthereof, and more particularly to the structure of a Peltier device forfixing an operating temperature of a semiconductor laser and atemperature control of the Peltier device.

2. Description of the Related Art

Presently, in order to fix a temperature of a laser diode (LD) device, aPeltier device is used in a laser diode module for high speed opticalcommunication, e.g., 2.4 G bit/sec, etc.

For example, a laser diode that emits a light beam is mounted on the topof a Peltier device, and the Peltier device performs a heating orcooling operation so as to fix the operating temperature of the laserdiode.

A Peltier device has a plurality of P-type semiconductor devices andN-type semiconductor devices that are alternately arranged in relationto each other. The top portions of the P-type and N-type semiconductordevices are combined with a ceramic cooling plane, and the bottomportions thereof are combined with a ceramic radiating plane.

In the cooling plane, a current output from a DC (direct current) powersupply flows from the N-type semiconductor devices to the P-typesemiconductor devices. Considering the above current flow as a flow ofelectrons, electrons flow from a P-type lower energy level to a N-typehigher energy level.

Consequently, the temperature at places combining the top portions ofthe P-type and N-type semiconductor devices with the cooling planedecreases by absorbing the surrounding thermal energy and thereby atemperature of the cooling plane decreases.

Conversely, in the radiating plane, the current flows from the P-typesemiconductor devices to the N-type semiconductor devices. Thus, theradiating plane is heated up by effects opposed to the above-mentioned.

As described above, a heating operation or cooling operation by aPeltier device can be controlled by varying a quantity of currentflowing therethrough or altering the direction of the current. A Peltiercontrol circuit controls a quantity or the direction of a currentflowing through a Peltier device by detecting the temperature of adevice, for example a laser diode in this example, combined with thePeltier device so that the temperature of the device is kept constant.

A conventional Peltier control circuit has a push-pull type drivingcircuit consisting of two pairs of transistors, arranged in a Darlingtonconfiguration. The driving circuit heats a Peltier device by outputtinga current thereto. Conversely, the driving circuit cools a Peltierdevice by inputting current. Also, in order to prevent an over-currentthat could destroy a Peltier device or cause thermal runaway, thedriving circuit has a current limiting circuit that limits a quantity ofa current flowing through a Peltier device by limiting a base currentapplied to the output transistors. Conventionally, a resistor is usedfor the current limiting circuit. In order to prevent such thermalrunaway, etc., the driving circuit has a dead zone in which the outputtransistors are turned OFF close to an alternating point between heatingand cooling operations.

The control of alternation between heating and cooling operations isperformed by comparing a voltage detected by a temperature sensor, whichmeasures the operating temperature of a Peltier device, with a referencevoltage a value of which is set within the dead zone. Therefore, in thiscase, it is impossible to control a temperature of a Peltier device whenthe voltage detected by the temperature sensor is within the dead zone.

The range of a dead zone is determined by the characteristics of atransistor (V_(BE)). Therefore, in the prior art there is a problem inthat the difference in temperature between a sensing temperature and acontrol temperature occurs within a dead zone. Further, there is anotherproblem in that the circuit loop stability for feedback control of thetemperature of a Peltier device decreases in the dead zone due to therepetition between heating and cooling operations so that a looposcillation may be caused.

Also, there is a problem in that when narrowing the dead zone by makingthe value of the current limiting resistor small, a loop oscillationalternately repeating between heating and cooling operations is morelikely, and further, an over-current flows when supplying power.

Further, there is a problem in that an oscillation phenomena that isdifferent from the above circuit loop oscillation occurs due to astructural factor of a conventional Peltier device. Namely, thecombination of inductive elements of lead wires connected to an inputand output of a laser diode and a capacitive element due to thestructure of a Peltier device as described above, produces a resonantfrequency point.

Therefore, conventionally, when using a laser diode module forhigh-speed optical communication, e.g., 2.4 G bit/sec, etc., there is aproblem in that the prescribed oscillation phenomena occurs in thefrequency range of optical communication.

SUMMARY OF THE INVENTION

To solve the above problems, the object of the present invention is toprovide a Peltier control circuit that has a current limiting circuitwith predetermined temperature characteristics by which the limitationof a current flowing through a Peltier device reaches a maximum valuenear room temperature. Thereby, a current applied to a Peltier devicefor heating and cooling operations is greatly limited or reduced nearroom temperature.

Also, the object of the present invention is to provide a Peltiercontrol circuit that enables fine temperature control of a Peltierdevice near room temperature by reducing the difference between startingtemperatures of heating and cooling operations.

Further, the object of the present invention is to provide a Peltierdevice that reduces or eliminates a stray-capacitive element due to thestructure of a Peltier device so as to prevent an oscillation phenomenaof an output so that the Peltier device can be applied to a laser diodemodule for high speed optical communication.

According to the present invention, there is provided a Peltier controlcircuit that detects the temperature of a device combined with a Peltierdevice and controls a current flowing through the Peltier device inaccordance with a detected temperature so as to keep the temperature ofthe device at a predetermined value. The circuit has a temperaturesensing section for detecting temperature of a device; a comparingsection for comparing a temperature detection value detected by thetemperature sensing section with a predetermined temperature referencevalue; a limiting section for providing a comparison output from thecomparing section with the limitation of a current flowing through thePeltier device and providing the prescribed limitation of the currentwith predetermined temperature characteristics; and a driving sectionfor providing the Peltier device with an input or output driving currentin accordance with the comparison output via the limiting section.

The limiting section limits the input or output driving current inaccordance with a variation in ambient temperature so as to compress aregion of a temperature dead zone in which the input and output drivingcurrents alternate with each other. The limiting section limits theoutput driving current by providing the comparison output from thecomparing section to the driving section via a resistor having apositive temperature coefficient, and limits the input driving currentby providing the comparison output from the comparing section to thedriving section via a resistor having a negative temperaturecoefficient.

The resistor having a positive temperature coefficient is seriallyconnected to a posistor and the resistor having a negative temperaturecoefficient is serially connected to a thermistor.

The comparing section includes a comparator for comparing a temperaturedetection voltage from the temperature sensing section with apredetermined reference voltage.

Also, according to the present invention, the comparing section includesa first comparator for comparing a temperature detection voltage fromthe temperature sensing section with a first reference voltagecorresponding to a starting point for driving the output driving currentand a second comparator for comparing a temperature detection voltagefrom the temperature sensing section with a second reference voltagecorresponding to a starting point for driving the input driving current.

The difference between the first reference voltage and the secondreference voltage is used to compress or expand a region of atemperature dead zone in which the input driving current alternates withthe output driving current.

The limiting section limits the output driving current by providing acomparison output from the first comparator to the driving section via aresistor having a positive temperature coefficient, and limits the inputdriving current by providing a comparison output from the secondcomparator to the driving section via a resistor having a negativetemperature coefficient.

Further, according to the present invention, there is provided a Peltierdevice having a cooling plane, a radiating plane and a plurality ofPeltier elements made of semiconductor that are sandwiched between thecooling and radiating planes, the device is characterized byelectrically combining the cooling plane with the radiating plane so asto eliminate a stray-capacitive element between the cooling andradiating planes. The electrical combination between the cooling andradiating planes is provided by coating at least one of the Peltierelements with metal. At least one of the Peltier elements is coated withmetal so as to have the structure of the Peltier device durable.

According to the present invention, it is possible to reduce thedifference between the operating temperature of a heating or coolingoperation and a sensor temperature thereof by having starting points ofthe heating and cooling operations close to each other. The limitingsection has temperature characteristics which provide the greatestlimitation of a current flowing through the Peltier device at roomtemperature. Thereby, it is possible to largely limit a current flowingthrough the Peltier device near room temperature at which a circuit loopbecomes unstable by e.g., circuit loop oscillation, etc. In this case, acurrent scarcely flows through the Peltier device even if alternatingbetween heating and cooling operations. Therefore, even if a circuitloop oscillation occurs, since a driving current applied to the Peltierdevice is very small and thereby the Peltier device cannot effectivelyperform heating and cooling operations, the circuit loop is totallystable. Also, for the same reasons, when supplying power at which acircuit loop is unstable, the excess current does not flow trough thePeltier device.

Further, according to the present invention, it is possible to reduce oreliminate a stray-capacitive element due to the structure of the Peltierdevice. Thereby, a resonant point caused by a capacitive element due tothe structure of the Peltier device and an inductive element due to alead line of the laser diode mounted on the cooling plane disappears oris moved out of a used bandwidth.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more clearly understood from thedescription as set forth below with reference to the accompanyingdrawings.

FIG. 1(A) is a top view of a laser diode module for high speed opticalcommunication.

FIG. 1(B) is a side view of a laser diode module for high speed opticalcommunication.

FIG. 2 is a perspective view of the conventional structure of a Peltierdevice used in a laser diode module.

FIG. 3 is an explanatory view for explaining the operation of athermoelectric heat pump due to the structure of a Peltier device.

FIG. 4 is a circuit diagram showing an example of a conventional Peltiercontrol circuit.

FIG. 5 is an explanatory view of a temperature dead zone in theconventional Peltier control circuit.

FIG. 6 is an equivalent circuit diagram corresponding to a wire boundingportion of a laser diode.

FIG. 7 is a diagram showing an example of frequency characteristics ofan optical output power output from a laser diode module.

FIG. 8 is a circuit diagram showing the first preferred embodiment of aPeltier control circuit according to the present invention.

FIG. 9 is a block diagram showing an example of a resistor having apositive temperature coefficient that is used as a limiting circuit.

FIG. 10 is a block diagram showing an example of a resistor having anegative temperature coefficient that is used as another limitingcircuit.

FIG. 11 is a diagram showing an example of temperature-resistancecharacteristics of limiting circuits shown in FIGS. 9 and 10.

FIG. 12 is a diagram showing an example of ambient temperature-Peltiercontrol current characteristics of a Peltier control circuit shown inFIG. 8.

FIG. 13 is a diagram showing an example of ambient temperature-sensortemperature characteristics of a Peltier control circuit shown in FIG.8.

FIG. 14 is a circuit diagram showing the second preferred embodiment ofa Peltier control circuit according to the present invention.

FIG. 15 is a diagram showing an example of the compression of a deadzone of a Peltier control circuit shown in FIG. 14.

FIG. 16 is a diagram showing an example of the expansion of a dead zoneof a Peltier control circuit shown in FIG. 14.

FIG. 17 is a perspective view showing an example of the basic structureof a Peltier device according to the present invention.

FIG. 18 is a diagram showing an example of frequency characteristics ofa laser diode module using the structure of a Peltier device shown inFIG. 17.

FIG. 19 is a diagram showing an embodiment of the structure of a Peltierdevice according to the present invention.

FIG. 20 is a diagram showing another embodiment of the structure of aPeltier device according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before describing the preferred embodiments according to the presentinvention, examples of the related art are provided with reference toFIGS. 1(A) to 7.

FIG. 1(A) is a top view of a laser diode module for high speed opticalcommunication.

FIG. 1(B) is a side view of a laser diode module for high speed opticalcommunication.

As shown in FIG. 1(B), a laser diode 2 is mounted on the top of thePeltier device 1 so as to emit a light beam. The Peltier device 1performs a heating or cooling operation to fix the operating temperatureof the laser diode 2.

FIG. 2 is a perspective view of the conventional structure of thePeltier device 1 used in a laser diode module.

FIG. 3 is an explanatory view for explaining the operation of athermoelectric heat pump based on the structure of a Peltier device.

In FIG. 2, the Peltier device 1 has a plurality of P-type semiconductordevices 7p and N-type semiconductor devices 7n that are alternatelyarranged in relation to each other. The top portions of the P-type andN-type semiconductor devices 7p and 7n are combined with a ceramiccooling plane 5, and the bottom portions thereof are combined with aceramic radiating plane 6.

As shown in FIG. 3, in the cooling plane 5 the current I output from DC(direct current) power supply 8 flows from the N-type semiconductordevices 7n to the P-type semiconductor devices 7p. Considering the abovecurrent flow as a flow of electrons, electrons flow from a P-type lowerenergy level to a N-type higher energy level.

Consequently, the temperature of a portion combining the N-typesemiconductor devices 7n and the P-type semiconductor devices 7p withthe cooling plane 5 (connecting taps) decreases by absorbing thesurrounding thermal energy and thereby the temperature of the coolingplane 5 decreases. Conversely, in the radiating plane 6 the current Iflows from the P-type semiconductor devices 7p to the N-typesemiconductor devices 7n. Thus, the radiating plane 6 is heated up byreverse operations described above. Incidentally, if connecting the DCpower supply 8 in the reverse direction and thereby changing thedirection of the current I (not shown in FIG. 3), the cooling plane 5 isheated up and the radiating plane 6 is cooled.

FIG. 4 is a circuit diagram showing an example of a conventional Peltiercontrol circuit.

FIG. 5 is an explanatory view of a temperature dead zone in theconventional Peltier control circuit.

FIG. 6 is an equivalent circuit diagram corresponding to a wire boundingportion of a laser diode.

As described above, a heating operation or cooling operation of aPeltier device can be controlled by varying a quantity of a current orchanging the direction thereof. A Peltier control circuit controls aquantity or the direction of a current flowing through the Peltierdevice by detecting a temperature of a device, e.g., a laser diode inthis example, etc., that is combined with a Peltier device.Consequently, the temperature of a device is fixed by using a negativefeed back loop control described above.

In FIG. 4, the thermistor 22 in the temperature sensor 11 detects thetemperature of a laser diode. A current detected by the thermistor 22 isprovided to the variable resistor 23 for fine controlling thetemperature together with a predetermined bias current flowing via theresistor 21. The variable resistor 23 converts those currents into avoltage corresponding to a detection temperature. The comparing section12 compares the voltage with a reference voltage corresponding to areference temperature by using an operational amplifier 28, and providesa comparison output signal to the driving section 13 at the next stage.The comparing section 12 uses a generally used inverted amplifier thatconsists of the operational amplifier 28 and resistors 24 and 25. Thecapacitor 26 is used for preventing an abrupt transition of an output ofthe operational amplifier by performing the integrating operation.

The driving section 13 uses a push-pull type output circuit thatconsists of two pairs of the transistors 32, 33 and 34, 35, and thetransistors 32, 33 or 34, 35 in each pair are connected by using aDarlington connection. The output circuit heats the Peltier device 1 byoutputting a current that flows through the Peltier device 1.Conversely, the output circuit cools the Peltier device 1 by inputtingthe current. Also, in order to prevent an over-current that coulddestroy the Peltier device 1 or cause a thermal runaway, the drivingsection 13 has a limiting circuit. The limiting circuit limits thequantity of a current provided to the Peltier device 1. Conventionally,the limiting resistors 29 and 30 as shown in FIG. 4 are used as thelimiting circuit.

In a conventional Peltier control circuit, in order to prevent such athermal runaway, etc., the driving section 13 has a temperature deadzone that makes the output transistors 33 and 35 both OFF close to analternating point between heating and cooling operations. FIG. 5 showsan example of a temperature dead zone in the conventional Peltiercontrol circuit.

However, the alternating control between heating and cooling operationsis performed by comparing a voltage detected by the temperature sensorsection 11 with a reference voltage that is set within a dead zone inthe comparing section 12. In this case, there is a problem in that it isimpossible to control the temperature of Peltier device 1 when thevoltage detected by the temperature sensor section 11 is within the deadzone.

The range of the dead zone is determined by the characteristics of atransistor (V_(BE)). Therefore, there is a problem in that a temperaturedetection error between a sensor temperature and a control temperatureoccurs in a range of the dead zone. Further, there is another problem inthat the circuit loop stability is reduced in the region because analternation between heating and cooling operations is repeated so that aloop oscillation could be caused.

Also, there is a problem in that by narrowing the temperature dead zoneby making the value of the limiting resistors 29 and 30 smaller, theloop oscillation wherein heating or cooling operation is alternatelyrepeated is more encouraged. In this case, another problem is caused inthat when supplying power, an over-current flows into a resistor.

Further, there is a problem in that an oscillation phenomena that isdifferent from the above loop oscillation occurs in relation to astructual factor of a conventional Peltier device as shown in FIG. 2.

FIG. 6 shows an equivalent circuit of a wire bound portion in the laserdiode module shown in FIGS. 1(A) and 1(B).

In FIG. 6, inductors L1 and L2 respectively direct inductive elements oflead wires connected to an input and output of the laser diode 2. Thecapacitor C_(TEL) directs a capacitive element to ground that is causeddue to the structure of a Peltier device. A resonant frequency f in thecircuit surrounded by a dotted line in the Figure is determined by anequation f=1/(2π×(L2×C_(TEL))^(1/2)). By substituting the observationvalues L2=1.4 mH and C_(TEL) =3 pF for the same signs in the equation,the resonance frequency f is 2.46 GHz.

FIG. 7 is a diagram showing an example of the frequency characteristicsof an optical output power output from a laser diode module shown inFIGS. 1(A) and 1(B).

From FIG. 7, it is found that a resonant point due to the capacitiveelement C_(TEL) exists.

As described above, conventionally when using a laser diode module forhigh-speed optical communication, e.g., 2.4 G bit/sec, etc., there is aproblem in that an oscillation phenomena occurs in a frequency rangeused for an optical communication.

Next, FIG. 8 is a circuit diagram showing the first preferred embodimentof a Peltier control circuit according to the present invention.

A basic circuit configuration of a Peltier control circuit is almost thesame as in FIG. 4. The configuration in FIG. 8 is simplified more thanthat in FIG. 4 so as to more clarify the present invention. Therefore,each operation of the circuit in FIG. 8 is not explained in thefollowing. Please see the explanation of the corresponding circuitsection in FIG. 4.

In FIG. 8, the limiting circuits 106 and 107 characterize the presentinvention. The limiting circuit 106 limits a base current applied to theoutput transistor 108 that controls an output of a driving current. Theoutput drive current heats the Peltier device 1. The limiting circuit107 limits a base current applied to the output transistor 109 thatcontrols an input of a driving current. The input current cools thePeltier device 1.

As shown in FIG. 8, the limiting circuit 106 consists of a resistorhaving a positive temperature coefficient. The temperaturecharacteristics of the resistor indicate low resistance at a lowtemperature. Conversely, the limiting circuit 107 consists of a resistorhaving a negative temperature coefficient. The temperaturecharacteristics of the resistor indicate low resistance at a hightemperature.

FIG. 9 is a block diagram showing an example of a resistor having apositive temperature coefficient that is used as a limiting circuit.

FIG. 10 is a block diagram showing an example of a resistor having anegative temperature coefficient that is used as another limitingcircuit.

FIG. 11 is a diagram showing an example of temperature-resistancecharacteristics of limiting circuits shown in FIGS. 9 and 10.

In FIG. 9, a posistor having a positive temperature coefficient isserially connected with a conventional output current limiting resistor116. In FIG. 10, a thermistor having a negative temperature coefficientis serially connected with a conventional output current limitingresistor 117.

In FIG. 11, as shown by a fine line, in a conventional limiting circuitthat consists of only a resistor (see FIG. 4), the resistance of theconventional limiting circuit does not change with temperature. Incontrast, a limiting circuit according to the present invention includesa resistance having a positive or negative temperature coefficient. Theformer has resistance-temperature characteristics as shown by a dottedcurved line and the latter has resistance-temperature characteristics asshown by a thick curved line.

In this case, a reference voltage is set to a value corresponding to acrossing point at which the dotted curved line intersects the thickcurved line at an ambient temperature 25° C.

Accordingly, a control current applied to the Peltier device 1 largelydecreases even if alternating between heating and cooling operationsnear an ambient temperature 25° C. Further, a current is greatly limitedwhen supplying power at ordinary temperature, at which a loop isgenerally unstable.

FIG. 12 is a diagram showing an example of ambient temperature-Peltiercontrol current characteristics of the Peltier control circuit shown inFIG. 8.

FIG. 13 is a diagram showing an example of ambient temperature-sensortemperature characteristics of the Peltier control circuit shown in FIG.8.

In FIGS. 12 and 13, a dotted line shows the characteristics of aconventional Peltier control circuit as shown in FIG. 4 and a solid lineshows the characteristics of a Peltier control circuit of the invention.As shown in FIGS. 12 and 13, it is found that according to the presentinvention a dead zone is compressed and thereby it is possible to keep atemperature of a laser diode device combined with a Peltier device,constant.

By the way, in FIG. 11, each control temperature for a heating operationand a cooling operation can be individually varied. This can be realizedby using a negative temperature coefficient resistor (thermistor) as apart of a current limiting resistor of the limiting circuit 106 or usinga positive temperature coefficient resistor (posistor) as a part of acurrent limiting resistor of the limiting circuit 107. Further, byadjusting a reference voltage applied to the comparator 105, it ispossible to desirably change the limits of a dead zone.

As shown in FIG. 13, it is possible to precisely compress a dead zone.Although the possibility for causing loop oscillation becomes larger inthis case, the overall loop is stable, because a limiting resistancebecomes larger and a quantity of an alternating current is very smallnear to an alternating point. Also, at an alternating point within adead zone the transistors 108 and 109 are both ON and a dark currentflows through the transistors 108 and 109. In such a case, powerconsumption can be reduced by a large limiting resistance. Furthermore,it is possible to prevent the Peltier device 1 from being destroyed bylimiting current when supplying power at an ordinary temperature.

FIG. 14 is a circuit diagram showing the second preferred embodiment ofa Peltier control circuit according to the present invention.

In FIG. 14, the difference between a second preferred embodiment and afirst preferred embodiment is in that the comparators 115, 125 and thereference voltages 1, 2 are individually arranged for each input oroutput Peltier control current.

In this circuit configuration, a dead zone can be desirably changed bysetting circuit parameters, e.g., a reference voltage, limitingresistor, etc. In contrast thereto, in a first embodiment shown in FIG.1, the compression of a dead zone is determined by the temperaturecharacteristics of the limiting circuits 106 and 107.

FIG. 15 is a diagram showing an example of the compression of a deadzone of a Peltier control circuit shown in FIG. 14.

FIG. 16 is a diagram showing an example of the expansion of a dead zoneof a Peltier control circuit shown in FIG. 14.

In FIG. 14, a heating operation of the Peltier device 1 is performed byusing the comparator 115 and the reference voltage 1, and the transistor108 is controlled by an output of the comparator 115. A coolingoperation of the Peltier device 1 is performed by using the comparator125 and the reference voltage 2, and the transistor 109 is controlled byan output of the comparator 125. The above two operations are performedindependently of each other, and thereby a temperature dead zone can bedesirably realized. The Peltier control circuit in this embodiment iseffective when controlling a wide range of temperature or using a devicethat can be controlled in the limits of a temperature excluding nearroom temperature. For the same reason as described above, the Peltiercontrol circuit can also control the temperature of a laser diode withvery small power consumption.

FIG. 17 is a perspective view showing an example of the basic structureof a Peltier device according to the present invention.

In FIG. 17, a stray-capacitive element (see C_(TEL) in FIG. 6) due to asandwich structure of the Peltier device 1 is reduced by electricallyconnecting the cooling plane 5 with the heating plane 6 by using metal9.

FIG. 18 is a diagram showing an example of the frequency characteristicsof a laser diode module using the structure of a Peltier device shown inFIG. 17.

Comparing the above characteristics with the conventionalcharacteristics shown in FIG. 7, it is found that an oscillationphenomena is clearly reduced or eliminated within a used bandwidth and adip portion in the frequency characteristics shown in FIG. 7 isremarkably improved.

FIGS. 19 is a diagram showing an embodiment of the structure of aPeltier device according to the present invention.

FIGS. 20 is a diagram showing another embodiment of the structure of aPeltier device according to the present invention.

FIG. 19 shows a case wherein a plurality of metal portions 9 arearranged in a Peltier device based on e.g., an experiment or thedistinctive feature of the structure, etc., so as to improve thefrequency characteristics of an output of a laser diode module.

FIG. 20 shows another case that metal portions 9 are arranged at fourcorners of a Peltier device so as to improve the frequencycharacteristics of an output of a laser diode module and furtherstrengthen the structure of a laser diode module.

As described above, according to the present invention, it is possibleto compress a temperature dead zone and keep a temperature of the laserdiode device constant by using a resistor having a positive temperaturecoefficient and using a resistor having a negative temperaturecoefficient.

Also, it is possible to desirably vary the limits of a temperature deadzone by enabling two kinds of resistance-temperature characteristics tobe set individually, or by independently adjusting two sets ofcomparator and reference voltages.

Further, according to the present invention, it is possible to preciselycontrol the temperature of a laser diode module by compressing a deadzone.

Also, it is possible to reduce power consumption by making a currentlimiting resistance large close to room temperature and an alternatingpoint.

Furthermore, according to the present invention, it is possible toreduce or eliminate a stray-capacitive element due to a sandwichstructure of the Peltier device by electrically connecting the coolingplane with the heating plane by using metal.

Also, it is possible to further improve the frequency characteristicsand further strengthen the structure of a laser diode module by havingat least one metal portion arranged in a Peltier device.

What is claimed is:
 1. A Peltier control circuit that detects atemperature of a device combined with a Peltier device and controls acurrent flowing through the Peltier device in accordance with thetemperature detected so as to keep the temperature of the device at apredetermined value, the circuit comprising:a temperature sensingsection for detecting said temperature of a device; a comparing sectionfor comparing a temperature detection value detected by said temperaturesensing section with a predetermined temperature reference value; alimiting section for providing a comparison output from said comparingsection with the limitation of a current flowing through the Peltierdevice and providing said limitation of the current with predeterminedtemperature characteristics; and a driving section for providing thePeltier device with an input or output driving current in accordancewith said comparison output via said limiting section.
 2. A Peltiercontrol circuit as set forth in claim 1, wherein said limiting sectionlimits said input or output driving current in accordance with thevariation of an ambient temperature so as to compress a region of atemperature dead zone in which said input driving current alternateswith said output driving current.
 3. A Peltier control circuit as setforth in claim 2, wherein said comparing section includes a comparatorfor comparing a temperature detection voltage from said temperaturesensing section with a predetermined reference voltage.
 4. A Peltiercontrol circuit as set forth in claim 3, wherein said limiting sectionlimits said output driving current by providing the comparison outputfrom said comparing section to said driving section via a resistorhaving a positive temperature coefficient.
 5. A Peltier control circuitas set forth in claim 3, wherein said limiting section limits said inputdriving current by providing the comparison output from said comparingsection to said driving section via a resistor having a negativetemperature coefficient.
 6. A Peltier control circuit as set forth inclaim 3, wherein said limiting section limits said output drivingcurrent by providing the comparison output from said comparing sectionto said driving section via a resistor having a positive temperaturecoefficient, and limits said input driving current by providing thecomparison output from said comparing section to said driving sectionvia a resistor having a negative temperature coefficient.
 7. A Peltiercontrol circuit as set forth in claim 4 or 6, wherein said resistorhaving a positive temperature coefficient includes the serial connectionof a resistor to a posistor.
 8. A Peltier control circuit as set forthin claim 5 or 6, wherein said resistor having a negative temperaturecoefficient includes the serial connection of a resistor to athermistor.
 9. A Peltier control circuit as set forth in claim 6,wherein said reference voltage corresponds to a cross point value atwhich said output driving current via said resistor having a positivetemperature coefficient intersects said input driving current via saidresistor having a negative temperature coefficient.
 10. A Peltiercontrol circuit as set forth in claim 1, wherein said comparing sectionincludes a first comparator for comparing a temperature detectionvoltage from said temperature sensing section with a first referencevoltage corresponding to a starting point for driving said outputdriving current and a second comparator for comparing a temperaturedetection voltage from said temperature sensing section with a secondreference voltage corresponding to a starting point for driving saidinput driving current.
 11. A Peltier control circuit as set forth inclaim 10, wherein the difference between said first reference voltageand said second reference voltage is used to compress or expand a regionof a temperature dead zone in which said input driving currentalternates with said output driving current.
 12. A Peltier controlcircuit as set forth in claim 11, wherein said limiting section limitssaid output driving current by providing a comparison output from saidfirst comparator to said driving section via a resistor having apositive temperature coefficient.
 13. A Peltier control circuit as setforth in claim 11, wherein said limiting section limits said inputdriving current by providing a comparison output from said secondcomparator to said driving section via a resistor having a negativetemperature coefficient.
 14. A Peltier control circuit as set forth inclaim 11, wherein said limiting section limits said output drivingcurrent by providing a comparison output from said first comparator tosaid driving section via a resistor having a positive temperaturecoefficient, and limits said input driving current by providing acomparison output from said second comparator to said driving sectionvia a resistor having a negative temperature coefficient.
 15. A Peltiercontrol circuit as set forth in claim 12 or 14, wherein said resistorhaving a positive temperature coefficient includes the serial connectionof a resistor to a posistor.
 16. A Peltier control circuit as set forthin claim 13 or 14, wherein said resistor having a negative temperaturecoefficient includes the serial connection of a resistor to athermistor.